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Levator ani

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Template:Infobox Muscle The levator ani is a broad, thin muscle, situated on the side of the pelvis.

It is attached to the inner surface of the side of the lesser pelvis, and unites with its fellow of the opposite side to form the greater part of the floor of the pelvic cavity.

It supports the viscera in pelvic cavity, and surrounds the various structures which pass through it.

In combination with the coccygeus muscle, it forms the pelvic diaphragm.

Parts

The levator ani is divided into three parts:

Origin and insertion of fibers

The levator ani arises, in front, from the posterior surface of the superior ramus of the pubis lateral to the symphysis; behind, from the inner surface of the spine of the ischium; and between these two points, from the obturator fascia.

Posteriorly, this fascial origin corresponds, more or less closely, with the tendinous arch of the pelvic fascia, but in front, the muscle arises from the fascia at a varying distance above the arch, in some cases reaching nearly as high as the canal for the obturator vessels and nerve.

The fibers pass downward and backward to the middle line of the floor of the pelvis; the most posterior are inserted into the side of the last two segments of the coccyx; those placed more anteriorly unite with the muscle of the opposite side, in a median fibrous raphé (anococcygeal raphé), which extends between the coccyx and the margin of the anus.

The middle fibers are inserted into the side of the rectum, blending with the fibers of the Sphincter muscles; lastly, the anterior fibers descend upon the side of the prostate to unite beneath it with the muscle of the opposite side, joining with the fibers of the sphincter ani externus and transversus perinei, at the central tendinous point of the perineum.

The anterior portion is occasionally separated from the rest of the muscle by connective tissue.

From this circumstance, as well as from its peculiar relation with the prostate, which it supports as in a sling, it has been described as a distinct muscle, under the name of Levator prostatæ.

In the female the anterior fibers of the Levator ani descend upon the side of the vagina.

Innervation

The levator ani muscles are mostly innervated by the pudendal nerve, perineal nerve and inferior rectal nerve in concert.[1] In addition, sacral spinal nerves (S3, S4) innervate the muscles directly as well (in ~70% [1] of people). Sometimes (in ~40% [1] of people) the inferior rectal nerve innervates the levator ani muscles independently of the pudendal nerve.

Tail-wagging in animals

The levator ani muscles, in quadruped animals with tails, are responsible for moving the tail around in the act of "wagging." These muscles are not as strong as their human equivalents, as tail-wagging is less demanding than the support function that the muscles serve in humans.[2]

Levator ani syndrome

Levator ani syndrome (also known as levator syndrome and proctodynia) is episodic rectal pain, caused by spasm of the levator ani muscle.[citation needed] The etiology is unknown.

Symptoms include a dull ache to the left 2 inches above the Anus or higher in the rectum and a feeling of constant rectal pressure or burning. The pain may also be felt in the low pelvis or perineum.[citation needed]

The discomfort may be relieved by walking or pelvic tightening exercises similar to Kegel exercises. Other treatments include massage of the muscle, warm baths, muscle relaxant medications, therapeutic ultrasound and biofeedback. Electrical stimulation of the levator ani muscle has been used to try to break the spastic cycle. Injection of botulinum toxin A has also been used.

Variants of levator ani syndrome include proctalgia fugax (fleeting pain in the rectum) and coccydynia (pain in the coccygeal region). Proctalgia fugax and levator ani syndrome have not been found to be of psychosomatic origin, although stressful events may trigger attacks.[citation needed]

Gallery

  • Gray236.png

    Right hip bone. Internal surface.

  • Gray402.png

    Coronal section of pelvis, showing arrangement of fasciæ. Viewed from behind.

  • Gray406.png

    Muscles of male perineum.

  • Levator ani.png
  • Gray539.png

    The arteries of the pelvis.

  • Gray837.png

    Sacral plexus of the right side.

  • Gray1076.png

    Iliac colon, sigmoid or pelvic colon, and rectum seen from the front, after removal of pubic bones and bladder.

  • Gray1077.png

    The posterior aspect of the rectum exposed by removing the lower part of the sacrum and the coccyx.

  • Gray1136.png

    Male pelvic organs seen from right side.

See also

Notes

  1. ↑ 1.0 1.1 1.2 Grigorescu BA, Lazarou G, Olson TR et al. (2008). "Innervation of the levator ani muscles: description of the nerve branches to the pubococcygeus, iliococcygeus, and puborectalis muscles". Int Urogynecol J Pelvic Floor Dysfunct 19 (1): 107–116. doi:10.1007/s00192-007-0395-8. PMID 17565421. 
  2. ↑ Sloan, Ethel (2001, p. 53). Biology of Women, Wisconsin: CENGAGE Delmar Learning. ISBN 0-7668-1142-5 (excerpt available here)

References

  • This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

External links

Template:Muscles of trunkhr:Mišić podizač čmarala:Musculus levator ani pl:Mięsień dźwigacz odbytu pt:Músculo levantador do ânus fi:Peräaukon kohottajalihas sv:Musculus levator ani

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